Amyotrophic lateral sclerosis (ALS) - commonly known as Lou Gehrig's disease - is a neuromuscular disorder. It's caused when the motor neurons that send electric "messages" from the brain to the spinal cord or from the spinal cord to the muscles are slowly being destroyed. These neurons are responsible for muscle movement in the body.
When the messages don't get through from the spinal cord, the muscles eventually lose strength and waste away. This process is called atrophy or amyotrophy. When signals from the brain to the spinal cord are blocked, the muscles become stiff and slow. This is called spasticity.
Up to 7 out of every 100,000 people get ALS. It's more common in men than women, with symptoms usually appearing between the ages of 50 and 75. About 10% of people with ALS have a family history of the disease. Life expectancy averages 2 to 5 years after diagnosis.
What causes ALS isn't known. Aside from a genetic predisposition in some cases, we don't really understand why the motor neurons are destroyed. One theory is that environmental factors such as heavy metal exposure can damage the nerve cells. Viral infections are yet another factor that may play a role in the development of ALS.
Another theory involves a chemical called glutamate, which is responsible for transmitting many of the messages between nerve cells in the brain. When glutamate isn't removed from the spaces between the nerve cells (called synapses), it builds up and causes an overflow of calcium into motor neurons. This eventually leads to destruction of nerve cells.
Motor neurons might also be damaged by free radicals. These molecules wreak havoc in cells and damage genetic material. In some people who have familial ALS, the gene for a particular enzyme that breaks down free radicals (superoxide dismutase) is abnormal. Free radicals might also be linked to environmental factors or excessive levels of glutamate.
The symptoms of ALS are caused by the destruction of motor neurons resulting in gradual deterioration of the muscles. Muscle atrophy often starts in the hands or feet and moves its way up the arms to the shoulders or up the legs to the hips.
The early symptoms of ALS include muscle weakness, clumsy hand movements, muscle stiffness, and difficulty performing tasks that require delicate movements of the fingers or hands. Muscular weakness in the legs may cause tripping and falling. As the muscles lose strength, some people experience muscle cramps, twitches, or spasms. When ALS progresses, more muscle groups become affected, leading to:
Only motor neurons - and therefore only muscles - are affected with ALS. Bladder and bowel muscles aren't usually involved, and the disease doesn't affect a person's mind or any of the 5 senses. People remain alert, but often lose the ability to take care of themselves. It can even become impossible to breathe without the help of a respirator.
There are several variants of ALS. Each has different symptoms and a different outcome.
Primary bulbar palsy: The initial or predominant symptoms are impaired speech or swallowing along with wasting of the tongue. The outcome is generally worse in this condition since swallowing and breathing are affected early in the course of the disease.
Progressive muscle atrophy: Muscle weakness and wasting are the principal features. Speech and swallowing are not affected and there is no spasticity. These individuals tend to have a slower course and better outcome.
Primary lateral sclerosis: The main feature is spasticity with no muscle atrophy. The outcome is usually somewhat better.